PERFORMANCE INVESTIGATION OF MULTILEVEL Z-SOURCE INVERTER FOR PHOTOVOLTAIC SYSTEMS

Abstract

A Z-source inverter (ZSI) has a unique ability to achieve single stage voltage buck-boost operation for energy conversion. This paper presents a three level ZSI using a single impedance network for photovoltaic (PV) application. A single LC impedance network is used between DC voltage source and neutral-point-clamped (NPC) inverter to achieve the desired stepped-up and stepped-down output voltage level. Alternative phase opposition and disposition (APOD) modulation technique with proper triplen offset and appropriate addition of time delay/advance is used to achieve the required boost in DC link voltage. A traditional MPPT technique is used to introduce a shoot-through interval in switching waveform to extract the maximum power from the PV panel. Traditional MPPT technique does not allow to boost the Z-network capacitor voltage more than the maximum power point (MPP) voltage of the PV array. This paper also presents a unified voltage control technique to track the MPPT and also maintains the desired Zsource capacitor voltage level. The design, implementation and control of single impedance network based multilevel ZSI for photovoltaic application is discussed and their MATLAB/Simulink simulation and results are presented in the later section of the paper to validate proposed control scheme in PV application.